The control of skeletal muscle relies on a complex integration between descending central input and information that originates from receptors that lie within peripheral tissue. The following investigations were performed to contribute to our understanding of this control. Study 1 ( Chapter 2 ) was designed to determine ( using the H - reflex ) if muscle spindle feedback is similar in the gastrocnemius and soleus. The strength of the H - reflex at rest and during contraction was compared between muscles. The results showed that the maximal H - reflex obtained at any level of contraction is larger in the soleus than in the gastrocnemius. We argue that along with the muscles having different structures and functions, the recruitment capabilities of their motoneurons are quite different. We also found that the maximal M - wave, which has for years been thought to be a consistent measure of maximal muscle activity, was quite variable within subjects during different conditions. Review of the maximal M - wave literature showed evidence that variability in this response did exist between conditions, but that the variability was rarely seen in pooled data, and was therefore not often reported. Study 2 ( Chapter 3 ) was developed to determine if experimental recording techniques, or analysis methods, could affect the magnitude of the maximal M - wave within subjects. The first finding of this study showed that the two most commonly used analysis methods ( peak - to - peak amplitude and area ) provided comparable results, and could not account for the differences seen in the maximal M - wave magnitude. The study did however suggest that the orientation of surface recording electrodes can significantly alter the recorded signal. We argue that although bipolar surface recording is considered superior to monopolar recording in its ability to record a clean signal, it has a large limiting factor, which we call " signal cancellation ". The third study ( Chapter 4 ) focused on the variability in M - wave strength in the gastrocnemius and soleus during a variety of ankle orientations and voluntary contraction levels. This study supported our previous work, and showed that when monopolar recording is used, consistent and significant differences exist in the strength on the M - wave obtained during different conditions that were not seen in bipolar recordings. It was concluded that the difference in maximal M - wave strength obtained during different muscle conditions may be related to a change in the recording electrode to muscle bulk relationship. This finding is important as M - wave strength is consistently used as a normalisation factor in reflex studies, and therefore variability in this measure may seriously affect the results obtained during muscle reflex investigations. The final study ( chapter 5 ) considered the size of the H - reflex, the level of background muscle activity, and the subjects ' weight distribution, during painful and non - painful conditions. We determined that these factors were not modified by pain induced in either agonist or antagonist muscles. The final chapter outlines the major findings from this work, highlights limitations to the research conducted using the H - reflex, and makes suggestions for future research in this area. / Thesis (Ph.D.)--School of Molecular and Biomedical Science, 2006.
| Identifer | oai:union.ndltd.org:ADTP/263701 |
| Date | January 2006 |
| Creators | Tucker, Kylie Jane |
| Source Sets | Australiasian Digital Theses Program |
| Language | en_US |
| Detected Language | English |
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